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Biomedical subjects

A Watts

Publications and source records attributed to A Watts.

At least 163 records · Page 9Linked to original sources

Electron spin resonance study of light-induced conformational changes in nitroxide labelled bovine rhodopsin.

Bovine rhodopsin was isolated in the unbleached form as a retinal disc membrane suspension and spin-labelled with 4-maleimido-2,2,6,6-tetramethylpiperidine-N-oxyl. Both conventional and saturation transfer electron spin resonance methods were used to investigate the sensitivity of the spin-label to conformational changes of rhodopsin induced by both transient and long-term exposure to light. The results indicate that the ESR methods do display sensitivity to such changes. An exponential decay curve with a time constant of 10 s was obtained by following the height of a single peak in the saturation transfer electron spin resonance spectrum in response to a single light flash.

Animals↗

A comparison of nucleolar organizer region staining and Ki-67 immunostaining in non-Hodgkin's lymphoma.

Eighty cases of non-Hodgkin's lymphomas were examined independently using the monoclonal antibody Ki-67 and an argyrophilic method for the demonstration of nucleolar organizer regions. The evidence that Ki-67 immunoreactivity may be used as a marker of cell proliferation is described and the nature of nucleolar organizer regions reviewed. The proportion of tumour cells with nuclear Ki-67 immunoreactivity and the mean number of nuclear organizer regions are shown to be linearly related (r = 0.86, P less than 0.001) although some scatter was observed. These data suggest that the mean number of nucleolar organizer regions may reflect the cellular kinetics of a tumour. This study also provides further evidence supporting the thesis that the mean nucleolar organizer region score is related to the histological grade of non-Hodgkin's lymphoma. Ki-67 immunostaining and nucleolar organizer region staining would seem to provide comparable data, at least in non-Hodgkin's lymphoma, but the latter method has the advantage of being applicable to conventionally fixed and processed paraffin sections.

Antibodies, Monoclonal↗

Salivary gland tumours studied by means of the AgNOR technique.

Difficulty is sometimes encountered in distinguishing between pleomorphic adenoma, adenoid cystic carcinoma and adenocarcinoma, especially in small biopsies from salivary glands. The argyrophil (AgNOR) staining technique for nucleolar organizer regions (NORs) has been applied to a series of benign and malignant salivary gland tumours. We studied 35 salivary gland tumours, 13 benign and 22 malignant. In all specimens clearly defined silver-stained intranuclear AgNOR dots were visible. The differences between the numbers of AgNORs in the benign and malignant groups, notably pleomorphic adenomas, adenoid cystic carcinoma and adenocarcinoma, were highly significant. In view of this difference we propose that the AgNOR staining technique is of diagnostic help in distinguishing between these salivary gland tumours.

Histocytochemistry↗

Preliminary investigation into the validity of dentists' decisions to restore occlusal surfaces of permanent teeth.

This study investigates the validity of the treatment decisions made by 10 hospital dentists, who examined the fissures of extracted teeth using a visual-only technique. The study shows that 8 of the 10 dentists were more likely to leave carious teeth unrestored than unnecessarily treat sound teeth. The authors suggest that this system of diagnosing occlusal caries is a satisfactory one in terms of its sensitivity and specificity.

Dental Caries↗

Spin-label electron spin resonance study of bacteriophage M13 coat protein incorporation into mixed lipid bilayers.

The major coat protein of bacteriophage M13 was incorporated in mixed dimyristoylphosphatidylcholine/dimyristoylphosphatidylglycerol (80/20 w/w) vesicles probed with different spin-labeled phospholipids, labeled on the C-14 atom of the sn-2 chain. The specificity for a series of phospholipids was determined from a motionally restricted component seen in the electron spin resonance (ESR) spectra of vesicles with the coat protein incorporated. At 30 degrees C and pH 8, the fraction of motionally restricted phosphatidic acid spin-label is 0.36, 0.52, and 0.72 for lipid/protein ratios of 18, 14, and 9 mol/mol, respectively. The ESR spectra, analyzed by digital subtraction, resulted in a phospholipid preference following the pattern cardiolipin = phosphatidic acid greater than stearic acid = phosphatidylserine = phosphatidylglycerol greater than phosphatidylcholine = phosphatidylethanolamine. The specificities found are related to the composition of the target Escherichia coli cytoplasmic membrane.

Coliphages↗

A deuterium and phosphorus-31 nuclear magnetic resonance study of the interaction of melittin with dimyristoylphosphatidylcholine bilayers and the effects of contaminating phospholipase A2.

The interaction of bee venom melittin with dimyristolphosphatidylcholine (DMPC) selectively deuteriated in the choline head group has been studied by deuterium and phosphorus-31 nuclear magnetic resonance (NMR) spectroscopy. The action of residual phospholipase A2 in melittin samples resulted in mixtures of DMPC and its hydrolytic products that underwent reversible transitions at temperatures between 30 and 35 degrees C from extended bilayers to micellar particles which gave narrow single-line deuterium and phosphorus-31 NMR spectra. Similar transitions were observed in DMPC-myristoyllysophosphatidylcholine (lysoPC)-myristic acid mixtures containing melittin but not in melittin-free mixtures, indicating that melittin is able to stabilize extended bilayers containing DMPC and its hydrolytic products in the liquid-crystalline phase. Melittin, free of phospholipase A2 activity, and at 3-5 mol% relative to DMPC, induced reversible transitions between extended bilayers and micellar particles on passing through the liquid-crystalline to gel phase transition temperature of the lipid, effects similar to those observed in melittin-acyl chain deuterated dipalmitoylphosphatidylcholine (DPPC) mixtures [Dufourc, E. J., Smith, I. C. P., & Dufourcq, J. (1986) Biochemistry 25, 6448-6455]. LysoPC at concentrations of 20 mol% or greater relative to DMPC induced transitions between extended bilayers and micellar particles with characteristics similar to those induced by melittin. It is proposed that these melittin- and lysoPC-induced transitions share similar mechanisms.(ABSTRACT TRUNCATED AT 250 WORDS)

Bee Venoms↗

Functional reconstitution of the integral membrane proteins of influenza virus into phospholipid liposomes.

The integral membrane proteins of influenza virus, a hemagglutinin and a neuraminidase, have been incorporated into liposomes composed of either phosphatidylcholine or a mixture of phosphatidylcholine and phosphatidylethanolamine (2:1 w/w) using detergent dialysis. The virus spike glycoproteins for reconstitution were selectively solubilized by using cetyltrimethylammonium bromide to leave a "core particle", which lacked a lipid bilayer but possessed quaternary structure as observed by electron microscopy. The viral spike proteins were combined with exogenous phospholipid in excess sodium cholate followed by exhaustive dialysis for 150 h. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed that only the viral glycoproteins were associated with all the complexes formed. The level of sodium cholate remaining after dialysis was shown to be reduced to less than 1 molecule per 80 protein molecules. Viral proteins reconstituted into dimyristoylphosphatidylcholine liposomes were shown to have retained hemagglutination, low-pH-dependent hemolysis, and neuraminidase activities and were associated with a lipid bilayer in two types of complexes with average lipid to protein mole ratios after sucrose density gradient purification of either 590:1 or 970:1. The bilayer vesicles formed were of similar sizes and were shown by negative-stain electron microscopy to be 150-300 nm in diameter with well-defined spikes on their surface. Reconstituted liposomes of dimyristoylphosphatidylcholine were found to be unstable with respect to their trapped volume and therefore were unsuitable for fusion studies, unlike complexes formed with phosphatidylcholine or a mixture of phosphatidylcholine/phosphatidylethanolamine derived from hen eggs.(ABSTRACT TRUNCATED AT 250 WORDS)

Dimyristoylphosphatidylcholine↗

The interaction of amino-deuteromethylated melittin with phospholipid membranes studied by deuterium NMR.

Melittin, deuteromethylated on each of the four amino groups (Gly-1 N alpha and Lys-7, 21, and 23 N epsilon), was prepared by reductive methylation using deuteroformaldehyde and NaBD3CN. Deuterium NMR spectra were obtained for the modified peptide (D-melittin) bound to phospholipid bilayers and erythrocyte ghosts. D-Melittin at 4 mol% (peptide:lipid) induced reversible transitions between extended bilayers and micelles at the phase-transition temperature in dimyristoylphosphatidylcholine (DMPC) bilayers. These changes in lipid morphology did not occur at 1 mol% D-melittin: DMPC and the peptide was highly motionally restricted in gel in gel-phase lipid.

Bee Venoms↗

Molecular exchange at the lipid-rhodopsin interface: spin-label electron spin resonance studies of rhodopsin-dimyristoylphosphatidylcholine recombinants.

The photoreceptor protein rhodopsin has been reconstituted with a single phospholipid species, dimyristoylphosphatidylcholine, at a range of different lipid/protein ratios, and the exchange rate at the lipid-protein interface has been determined from the electron spin resonance spectra of spin-labeled phosphatidylcholine. For recombinants with lipid/protein ratios in the range 41:1 to 102:1 (mol/mol), the electron spin resonance spectra of 1-acyl-2-[14-(4,4-dimethyloxazolidine-N-oxyl)stearoyl]-sn-glycero-3- phosphocholine consist of a fluid component similar to that found in pure lipid bilayers and a motionally restricted component corresponding to lipids whose motion is reduced by interaction with the intramembranous surface of rhodopsin. The relative proportion of the motionally restricted component increases with increasing protein content in the complex. Spectral subtraction with fluid and motionally restricted components (from fluid- and gel-phase lipid, respectively), which best fit the apparent components in the complex, reveals that 22 +/- 2 lipids per 39,000-dalton protein are motionally restricted, independent of lipid/protein ratio and of temperature. Simulation of the two-component spectra with the exchanged-coupled Bloch equations gives values for both the fraction of motionally restricted component and the exchange rate between the two components. Using fixed motionally restricted and fluid component line shapes at a given temperature, it is possible to obtain a consistent description of the lipid/protein ratio dependence of the spectra at each temperature. The number of motionally restricted lipids obtained by simulation, allowing for exchange, is 23 +/- 3 per 39,000-dalton protein, again independent of temperature and of lipid/protein ratio.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

Nuclear magnetic resonance methods to characterize lipid-protein interactions at membrane surfaces.

Specific molecular interactions that determine many of the functions of a biomembrane have a high probability of occurring at the surface of that membrane. However, unlike their hydrophobic core, the polar-apolar interface of biomembranes has been somewhat neglected experimentally. Reasons for this are that the chemical heterogeneity encountered makes a simple description difficult and that probing the membrane surface often involves a perturbation of those very interactions being studied. Classical methods for obtaining structural information about biomolecules, including X-ray diffraction, electron microscopy, and more recently high-resolution 2D nuclear magnetic resonance techniques are inappropriate for all but the simplest of membrane problems. In an effort to throw light on how membrane surfaces are organized, both architecturally and dynamically, protons in lipids and proteins have been selectively replaced by deuterons and the resultant deuterium NMR spectrum analyzed to give structural and dynamic information about the molecular associations between a range of membrane components. In principle, lipids, proteins, and oligosaccharides can be studied by this method and the information gained related to biochemical integrity and function. With one or two notable exceptions, the majority of the studies reported so far have been on model systems. A comprehensive review of the literature will not be presented here. However, protein-lipid molecular specificity in membranes, peptide-induced lateral separation, and the ionization behavior of deuterated phospholipids and peripheral proteins will all be demonstrated predominantly using deuterium NMR methods. Some suggestions for future work are also presented.

Magnetic Resonance Spectroscopy↗

Bacterial contamination as a factor influencing the toxicity of materials to the exposed dental pulp.

Three materials, which had been previously found to be toxic when applied as pulp-capping agents in conventional rat molar pulps, were retested in germ-free rats. All produced much more favorable responses in the pulp, with a lack of inflammation and the presence of dentine bridges in the majority of teeth. It appears that much of the pulp damage previously attributed to the chemical toxicity of materials may be caused by the presence of bacteria. The design of studies intended to evaluate the response of the pulp to materials should include staining techniques that will detect the presence of bacteria on the floors of test cavities.

Aluminum Hydroxide↗

Direct determination by 2H-NMR of the ionization state of phospholipids and of a local anaesthetic at the membrane surface.

Protonation and deprotonation of the primary amino group of phosphatidylethanolamine, and of the lipid phosphate groups of phosphatidylethanolamine with phosphatidylcholine, have been observed directly and isothermally in equimolar mixed fluid bilayers of the two phospholipids. In addition, the acid-base titration of the secondary amino group of the local anaesthetic, tetracaine, whilst partitioned into the bilayers, has also been determined. Here we show how studies by deuterium nuclear magnetic resonance of non-perturbing deuterons, specifically placed at the membrane polar-apolar interface, can give direct information about the electrostatics at a membrane surface.

Chemical Phenomena↗